Recirculation filter for an electronic enclosure

ABSTRACT

A filter assembly for use in an electronic enclosure is provided. The filter assembly includes a highly permeable scrim that defines an elongate enclosure with an inlet at a first end and a closed second end, wherein an electrostatic filtration media is disposed within the elongate enclosure.

This application is a continuation of U.S. application Ser. No.13/831,458, filed March 14, 2013, which claims the benefit of U.S.Provisional Application Serial No. 61/681,618 filed Aug. 10, 2012, thecontents of which are herein incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to filters for use in electronicenclosures. In particular, the invention is directed to filters forremoving contaminants circulating within the interior of an electronicenclosure.

BACKGROUND

Contaminants within an electronic enclosure, such as a hard disk driveenclosure, can reduce the efficiency and longevity of the componentswithin the enclosure. Contaminants can include chemicals andparticulates, and can enter the hard drive enclosure from externalsources, or be generated within the enclosure during manufacture or use.The contaminants can gradually damage the drive, resulting indeterioration of drive performance and even complete failure of thedrive. Consequently, data storage systems such as hard disk drivestypically include one or more filters capable of removing or preventingentry of particulate and/or chemical contaminants in the air within thedisk drive enclosure. One type of such filter is a recirculation filter,which is generally placed such that it can filter out contaminants fromthe path of airflow caused by rotation of one or more disks within thedisk drive. Although existing recirculation filters can remove manycontaminants, a need exists for improved performance at removing certaincontaminants, in particular, large particulate contaminants.

SUMMARY OF THE INVENTION

The present application is directed, in part, to filter assemblies foruse in an electronic enclosure. The filter assemblies are designed toremove particulate contaminants circulating within the electronicenclosure. In particular, the filter assemblies are constructed andarranged so as to effectively reduce the particulate contaminant levelsby capturing the particles and preventing their release back into theelectronic enclosure. Typically the filter assemblies are constructedwith a media geometry that aids in the capture of particles, and whichavoids reflection of particles out of the filter assemblies.

The filter assemblies further include, in various embodiments, mediaconfigurations that are further designed to promote the capture ofparticulate contaminants. These media configurations include, forexample, constructions with an electrostatic media overlaying all orpart of a scrim material on the interior of the filter assembly. Withoutintending to be bound by a specific mechanism of operation, it isbelieved that the electrostatic helps prevent particles from strikingthe media and then bouncing off (often referred to as reflection), whichcan otherwise occur with exposed scrim materials. The electrostatic mayalso further help in capturing the particles to prevent their continuedcirculation through the electronic enclosure.

In an example embodiment, the filter assembly includes a media structurethat includes an open front end, a closed rear end, and an internalrecess between the open front end and closed rear end. Permeable filtermedia forms at least a portion of the recess. The recess is typicallyrelatively deep, in some cases as deep or deeper than the width of thefilter assembly. Thus, the recess can be conical or column shaped (forexample) in some embodiments. This recirculation filter structure withan internal recess promotes the capture and retention of particulatecontaminants by having a large open front surface area while having aneven larger interior surface area comprising filter media. The interiormedia surface is generally angled relative to the air flow direction sothat particles hit the media at an acute angle such that they can eitherbe retained by the media at the point of initial contact or slowed downsufficiently to be retained deeper inside the filter assembly.

In some implementations at least 50 percent of the surface area of theinternal recess has an angle to the opening that is less than or equalto 45 degrees. At least 75 percent of the surface area of the internalrecess has an angle to the opening that is less than or equal to 45degrees in some example implementations. Optionally at least 50 percentof the surface area of the internal recess has an angle to the openingthat is less than or equal to 30 degrees. In some example embodiments atleast 75 percent of the surface area of the internal recess has an angleto the opening that is less than or equal to 30 degrees.

In certain implementations the internal recess of the filter assemblyhas a ratio of maximum depth to maximum diameter of the open front faceof at least 1.0, but this maximum depth to maximum diameter ratio canvary, and is often higher than 1.0, such as higher than 1.25, 1.5, 1.75;or 2.0, for example. The internal recess of the filter assembly can havean internal surface area that is at least 2 times the area at the openfront face, in other implementations at least 3 times the area at theopen front face, and in other implementations at least 4 times the areaat the open front face, at least 4 times the area of the open face insome implementations, or at least 5 or 6 times the area at the openfront face in certain embodiments.

In some embodiments, the permeable scrim material comprises woven ornon-woven material, such as polypropylene fibers. The scrim material canhave, for example, a permeability of between about 100 ft./min. at 0.5inches of water and about 800 ft./min. at 0.5 inches of water in someembodiments. In certain embodiments the scrim material has apermeability of between about 250 ft./min. at 0.5 inches of water andabout 600 ft./min. at 0.5 inches of water. The scrim material has apermeability of between about 300 ft./min. at 0.5 inches of water andabout 500 ft./min. at 0.5 inches of water in some exampleimplementations. It will be understood that suitable scrim material canhave, for example, a permeability of more than 100 ft./min. at 0.5inches of water; more than 250 ft./min. at 0.5 inches of water; or morethan 300 ft./min. at 0.5 inches of water. Suitable scrim material canhave, for example, a permeability of less than about 800 ft./min. at 0.5inches of water in some embodiments; less than 600 ft./min. at 0.5inches of water in some embodiments; or less than 500 ft./min. at 0.5inches of water in some embodiments.

The electrostatic material can contain various fibers, and is optionallya mixed fiber media comprising polypropylene and acrylic fibers. Theelectrostatic material has, for example, a permeability of between about250 ft./min. at 0.5 inches of water and about 750 ft./min. at 0.5 inchesof water. The electrostatic material can have a filtering efficiency ofabout 20% to about 99.99% for 20 to 30 micron particulate contaminantsin some embodiments. Suitable electrostatic can, for example, have afiltering efficiency of greater than 20% for 20 to 30 micron particulatecontaminants; greater than 40% for 20 to 30 micron particulatecontaminants; or greater than 60% for 20 to 30 micron particulatecontaminants. The electrostatic material can have in some exampleimplementations a filtering efficiency of less than 99.99% for 20 to 30micron particulate contaminants; less than 80% for 20 to 30 micronparticulate contaminants; or less than 60% for 20 to 30 micronparticulate contaminants.

The above summary of the present invention is not intended to describeeach discussed embodiment of the present invention. This is the purposeof the figures and the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully explained with reference to thefollowing drawings.

FIG. 1 is a simplified perspective view of a disk drive assembly,showing the top of the disk drive assembly removed.

FIG. 2 is a perspective view of a filter assembly constructed andarranged in accordance with an implementation of the invention.

FIG. 3 is a side elevation view of a filter assembly constructed andarranged in accordance with the implementation of the invention shown inFIG. 2.

FIG. 4 is a front elevational view of a filter assembly constructed andarranged in accordance with the implementation of the invention shown inFIG. 2.

FIG. 5A is a cross-sectional view of the filter assembly of FIG. 3 takenalong line 3-3′.

FIG. 5B is a detail of a portion of the filter assembly shown in crosssection in FIG. 5A, showing the media layers.

FIG. 6 is a partial top plan view of disk drive assembly containing afilter assembly constructed and arranged in accordance with an exampleimplementation of the present invention.

FIGS. 7A-7D are schematic depictions showing a method of making a filterassembly as described herein.

FIG. 8 is a cross sectional view of a filter assembly made in accordancewith an implementation of the invention, the filter assembly having aninclined opening.

FIG. 9 is a perspective view of a filter assembly made in accordancewith an implementation of the invention, the filter assembly having aplurality of filtration recesses.

FIG. 10 is a cross sectional view of the filter assembly of FIG. 9 takenalong lines 9-9′

FIGS. 11A-11I are schematic depictions showing a method of making afilter assembly as described herein.

FIG. 11J is chart depicting a method of making a filter assembly asdescribed herein

FIGS. 12A-12G are schematic depictions showing a method of making afilter assembly as described herein.

FIG. 12H is chart depicting a method of making a filter assembly asdescribed herein

While principles of the invention are amenable to various modificationsand alternative forms, specifics thereof have been shown by way ofexample in the drawings and will be described in detail. It should beunderstood, however, that the intention is not to limit the invention tothe particular embodiments described. On the contrary, the intention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the disclosure and claims.

DETAILED DESCRIPTION

Various filtering systems are known that are used to reduce or removecontaminants from disk drive assemblies, as well as other electronicenclosures. In particular, recirculation filters are often used toreduce or remove particulate and/or chemical contaminants that haveentered a disk drive enclosure or been generated during use of the diskdrive. A typical recirculation filter includes a filter element that ispositioned in the path of air currents induced by disk rotation suchthat contaminants present in the air current are subject to filtration.

However, not all particles that come into contact with the filter aresuccessfully captured. The face velocity of many available filterassemblies is very high, which can increase particle momentum. The highmomentum can result in particulate contaminants “reflecting” or“bouncing” off the filter surface, rather than being entrapped by thefilter. This phenomenon can be referred to as “particle bounce.” Exposedscrim material, which makes up the surface of many existingrecirculation filters, can be a particular problem because particlesbounce off the scrim fibers at relatively high rates. Thus, a needexists for an improved recirculation filter that can capture evenparticulate contaminants having relatively high momentum.

A filter assembly for use in an electronic enclosure is described hereinto provide improved particulate contaminant removal. In an exampleembodiment, the filter assembly includes a media structure having anopen front face, a closed rear face, and an internal recess between theopen front face and closed rear face. A permeable scrim material canform at least a portion of the media structure. An electrostaticmaterial is disposed within the internal recess of the filter assembly,the electrostatic material at least partially covering the permeablescrim. In an example embodiment the electrostatic material will overlayall or most of the permeable scrim. In some embodiments theelectrostatic material and scrim are combined together before productionof the filter assembly (such as, for example, by lamination, heatbonding, or light calendaring) and subsequently formed into a mediastructure that creates at least a portion of the filter assembly.

In certain implementations the internal recess of the filter assemblyhas a ratio of maximum depth to maximum diameter of the open front faceof at least 1.0, but this maximum depth to maximum diameter ratio canvary, and is often higher than 1.0, such as 1.25, 1.5, 1.75; or 2.0, forexample. The internal recess of the filter assembly can have an internalsurface area that is at least 2 times the area at the open front face,in other implementations at least 3 times the area at the open frontface, and in other implementations at least 4 times the area at the openfront face, or at least 5 or 6 times the area at the open front face.

In some embodiments, the permeable scrim material comprises woven ornon-woven material, such as polypropylene fibers. The scrim material canhave, for example, a permeability of between about 100 ft./min. at 0.5inches of water and about 800 ft./min. at 0.5 inches of water in someembodiments. In some embodiments the scrim material has a permeabilityof about 250 ft./min. at 0.5 inches of water and about 600 ft./min. at0.5 inches of water. In yet other implementations the scrim material hasa permeability of about 300 ft./min. at 0.5 inches of water and about500 ft./min at 0.5 inches of water, It will be understood that suitablescrim material can have, for example, a permeability of more than 100ft./min. at 0.5 inches of water; more than 250 ft./min. at 0.5 inches ofwater; or more than 300 ft./min. at 0.5 inches of water. Suitable scrimmaterial can have, for example, a permeability of less than about 800ft./min. at 0.5 inches of water in some embodiments; less than 600ft./min. at 0.5 inches of water in some embodiments; or less than 500ft./min. at 0.5 inches of water in some embodiments.

The electrostatic material can contain various fibers, and is optionallya mixed fiber media comprising polypropylene and acrylic fibers. Theelectrostatic material has, for example, a permeability of between about250 ft./min. at 0.5 inches of water and about 750 ft./min. at 0.5 inchesof water. The electrostatic can have a filtering efficiency of about 20%to about 99.99% for 20 to 30 micron particulate contaminants in someembodiments. Suitable electrostatic can, for example, have a filteringefficiency of greater than 20% for 20 to 30 micron particulatecontaminants; greater than 40% for 20 to 30 micron particulatecontaminants; or greater than 60% for 20 to 30 micron particulatecontaminants. The electrostatic can have in some example implementationsa filtering efficiency of less than 99.99% for 20 to 30 micronparticulate contaminants; less than 80% for 20 to 30 micron particulatecontaminants; or less than 60% for 20 to 30 micron particulatecontaminants.

Now, in reference to the drawings, FIG. 1 is a simplified perspectiverepresentation of a disk drive 100. The disk drive 100 includes body 102that forms an enclosure 104. In an example embodiment, one or morerotatable magnetic disks 106 are positioned within the enclosure 104.The rotation of the drive is shown by arrows (although opposite rotationis alternatively possible). Other disk drive components, such as aread-write head and wiring can be incorporated into an armature 108.

An example embodiment of a filter assembly 200 is shown in FIGS. 2, 3and 4. As shown in FIG. 2, the filter assembly comprises an open frontend 202, and a closed rear end 204. The filter assembly 200 includes anelongate media structure 206 between the front end 202 and rear end 204,the elongate media structure 206 being primarily made of filter media,such as in an example embodiment, a scrim on one side with anelectrostatic material on the other side. Preferably the electrostaticmedia is located on the interior side of the elongate media structure206. Sidewalls forming the elongate media structure extend from the openfront end 202 to the closed rear end 204. In the implementation shown,the elongate media structure 206 is secured to a frame 208. The frame208 can be, for example, a metal or plastic support that secures themedia structure 206 and may aid in installation into an electronicenclosure.

This example filter assembly 200 is also shown in FIG. 3, in sideelevational view, and in FIG. 4 in front view (taken from the front end202). Measurement of the diameter “D” of the filter assembly 200 istaken along the open interior of the filter assembly 200 at the frontend 202. The opening can be generally circular as shown in FIG. 2. Inthe alternative, the opening can be oval shaped, otherwise non-circular,and rectangular or otherwise the approximate shape of a polygon, forexample. In many embodiments, however, the opening will be circular,semi-circular, ovular, semi-ovular, or otherwise have a generallyrounded front opening. This generally rounded front opening allows forease of manufacture of the filter assembly 200.

In FIG. 4, two diameters are shown: D_(x) and D_(y). D_(x) refers to thelongest diameter across the open front end 202, and D_(y) refers to adiameter at the open front end 202 that is perpendicular to D_(x).Diameter of non-circular openings can be measured by taking an averagediameter (such as by averaging the D_(x) and D_(y) diameters), or bymeasuring a maximum diameter, such as D_(x). In general, at least one ofD_(x) and D_(y) is between about 0.25 and about 1 inches. Generally thelength “L”, shown in FIG. 2, of the filter assembly 200 is greater thanthe diameter of the filter assembly 200. Specifically, the length L istypically longer than the longer of D_(x) and D_(y). In someimplementations length L is longer than the average of D_(x) and D_(y)In one embodiment, the length “L” of the filter assembly 200 can be atleast 1.5, 2, or 3 times the longer of the diameters D_(x) and D_(y) ofthe filter assembly. The length L can be, for example, between about0.25 and about 2 inches.

The open front end 202 is generally positioned upstream from the closedrear end 204 with respect to airflow within the electronic enclosure.The elongate shape of the filter assembly 200, in particular theelongate media structure 206, increases the surface area of filtrationmedia to which the airflow is exposed, thereby increasing the amount ofparticles that are captured by the filter assembly 200 duringfiltration, as well as entrapping particles with higher mass ormomentum. Furthermore, the construction of the filter assembly, with alarge front opening, and an even larger media surface area in theelongate media structure 206, reduces pressure restriction of the filterassembly 200.

In an example embodiment, the filter assembly 200 has a substantiallycylindrical configuration. As used herein, the term “substantiallycylindrical” means that the front end 202 and rear end 204 of the filterassembly are substantially circular and the sidewalls 212 (FIG. 3) ofthe filter assembly 200 are parallel or substantially parallel. Inanother embodiment, the filter assembly 200 has a substantially conicalor parabolic configuration. As used herein, the term “substantiallyconical” or “substantially parabolic” means that the open front end 202converges towards the closed rear 204 end of the filter assembly 200.Other filter assembly configurations are also possible, in particularother elongate configurations having an ovoid, square, rectangular orother cross-sectional shape either with or without converging sidewalls,and would fall within the scope of the invention.

While not wishing to be bound by theory, it is believed that the use ofan open filtration construction with large media surface area reducessurface velocity of the particulate contaminants and can therebyincrease particle capture. In an example embodiment, the filtrationmedia has a 20 micron to 30 micron filtering efficiency of about 20% toabout 99.99%. The permeability of the filtration media is generallybetween about 250 ft./min. at 0.5 inches of water and about 750 ft./min.at 0.5 inches of water. The basis weight is generally between about45gm/m² and about 165 gm/m².

FIG. 5A shows a cross section of the filter assembly 200 of FIGS. 2 to4. FIG. 5A shows the angle alpha between the side wall 212 and a line214 perpendicular to the front end 202 of the filter assembly 200,corresponding to the path of a particle flowing perpendicular to thefront end 202 of the filter assembly. This angle alpha is typically lessthan 45 degrees over the majority of the sidewall forming the elongatemember 206, and alternatively less than 30 degrees or less than 15degrees over the majority of the media. FIG. 5B shows a simplifiedenlarged view of a cross section of the filter assembly, showing anelectrostatic layer 220 and a support layer 222 (such as a scrim layer).The line 214 at angle alpha is also shown, depicting the relativelyacute angle (e.g. preferably less than 45 degrees) at which particlesthat are travelling perpendicular to the opening will strike the media.In the alternative, the media forming the filter assembly 200 can beformed of a single layer, or more than two layers. Also, in certainembodiments a portion of the media is single layer, and a portion of themedia has more than one layer.

In one embodiment, the filtration media forming the elongate portion 206includes electrostatic fibers. The term “electrostatic fibers,” as usedherein, refers to fibers that contain an electric charge. One advantageof including electrostatic fibers in the filter assembly 200 is that thefilter is not only able to mechanically trap contaminants, but is alsoable to exert an electrostatic force on contaminants that containelectric charges, thereby increasing the amount of contaminants that areremoved from the airstream. The electrostatic media can be triboelectricmedia, electret media, or any other media that can be charged, or thatdepends on charging as the main mechanism for particle removal. Inexample embodiments, the electrostatic media include triboelectricfibers. Triboelectric fibers are known and can be formed, for example,using a mixture of (1) polyolefin fibers such as polyethylene,polypropylene or ethylene and propylene copolymers, with (2) fibers ofanother polymer, for example, fibers containing hydrocarbon functionssubstituted by halogen atoms, such as chlorine or polyacrylonitrilefibers. In general, the polyolefin fibers and the other polymer fibersare included in the electrostatic media at a weight ratio between about60:40 or about 20:80 or about 30:70.

FIG. 6 shows a filter assembly 200 installed within an electronicenclosure 100 (only a corner of the enclosure 100 is depicted). Thefilter assembly 200 is oriented so that the open front end 202 isdirected toward the air stream generated by the rotating disk 106(depicted directionally by arrows). In the embodiment shown, a baffle114 is present to aid in the direction of air into the open front end202 of the filter assembly 200. The filter assembly 200 can be placedwithin the electronic enclosure such that the baffle 114 directs airinto and through the open front end 202. In certain implementations thebaffle 114, along with any mounting elements (such as a frame 208 shownin FIG. 2) or other portions of the housing form a channel that directsair into the open front end 202. In other implementations the filterassembly 200 is positioned in a flowing air stream without a channeldirecting air into it, or only an open sided channel that only partiallydirects air into the filter assembly 200.

One method for making a filter assembly as described herein is shownschematically in FIG. 7A to 7D. In this method, a sheet of scrimmaterial 302 having a length “L_(m)” and a width “W_(m)” is provided(FIG. 7A). The scrim material 302 is rolled along an axis substantiallyparallel to the length L_(m) of the scrim to form a cylindrical orconical article 306 (FIG. 7B). The scrim 302 is sealed along the lengthL_(m) of the article, for example, using an adhesive or by welding. Anend 304 of the article is then sealed to form a closed article thatdefines a chamber having a length “L_(A)” (FIG. 7C). The opposite end302 is then adhered to a frame 308, for example, using an adhesive, orby welding (FIG. 7D) and a filtration media, for example, anelectrostatic filtration media is introduced into the interior of theelongate member formed by the process.

FIG. 8 is a cross sectional view of a filter assembly 400 made inaccordance with an alternative implementation of the invention, thefilter assembly having an inclined opening 402 secured to a frame 408.Media is configured in an elongate member 406. The filter assembly 400has a length “L” measured from the middle of the opening, and diameter“D”. The overall configuration and performance is similar to that ofassembly 200 discussed above, only the open end 402 and frame 408 areangled relative to the elongate media member 406. Also, the filterassembly 400 has sidewalls 410 and 412 of different lengths from oneanother.

FIG. 9 is a perspective view of a filter assembly 500 made in accordancewith an implementation of the invention, the filter assembly 500 havinga plurality of filtration recesses 520. FIG. 10 is a cross sectionalview of the filter assembly of FIG. 9 taken along lines 9-9′, showingthe filter assembly 500 with recesses 520. The cross section shows therelative length “L” and diameter “D” of the filter assembly 500.Typically the length L is at least 1.5 times the diameter D, morecommonly the length L is at least 2.0 times the diameter D. In someimplementations the length L is at least 3.0 times the diameter D. Thefilter assembly 500 will typically have a sealed back end 522 covered bymedia, such as a scrim material or an electrostatic material covering ascrim material.

A method for making a filter assembly as described herein is shownschematically in FIGS. 11A to 11I. In the example method, a sheet offilter material 1102 is provided (FIG. 11A). The sheet of filtermaterial 1102 can comprise an electrostatic layer 1120 and a supportlayer 1122 (such as a scrim layer). The sheet of filter material 1102can be pressed into a desired configuration. The method can comprise theuse of a nest 1104. The nest 1104 can comprise a recess 1106 (FIG. 11B).The recess 1106 can be shaped similarly to the desired final shape ofthe filter assembly. The method can comprise the use of a horn 1108(FIG. 11C). The horn 1108 can have a similar shape as the desired finalshape of the filter assembly. The sheet of filter material 1102 can bepositioned between the horn 1108 and a nest 1104 (FIG. 11D).

The horn 1108 can be moved into a position where the horn 1108 is atleast partially disposed within the recess 1106 of the nest 1104. Thefilter material 1102 can conform to the outer shape of the horn 1108 andthe shape of the recess 1106. In an embodiment, sufficient force isapplied to the filter material 1102 to permanently deform the filtermaterial 1102. A small amount of heat or sonic energy is applied to meltsome of the media to form a border 1103 that helps retain the shape.

The horn 1108 can be removed from a position where the horn 1108 is atleast partially disposed within the recess 1106 (FIG. 11E) and thefilter material 1102 can remain in a configuration closely resemblingthe configuration the filter material 1102 was in when the horn 1108 wasat least partially disposed within the recess 1106.

A screen layer 1110 can be placed on top of the filter material 1102,such as to sandwich the filter material 1102 between the nest 1104 andthe screen layer 1110 (FIG. 11F). The screen layer 1110 can be welded,fused or otherwise bonded to the filter material 1102. In an embodiment,the filter material 1102 comprises an electrostatic layer 1120 and asupport layer 1122 and when the screen layer 1110 is welded to thefilter material 1102, the electrostatic layer 1120 can be welded to thesupport layer 1122. The filter assembly can be welded such as along line1114. The filter assembly can be welded on a plurality of lines 1114.Any excess material beyond the weld line (FIG. 11H) can be removed fromthe filter assembly, such as by trimming, resulting in a filter assembly1100 (FIG. 11I).

The screen layer 1110 can partially cover the open end of the filterassembly. The screen layer 1110 can allow air to pass through the screenlayer and into the recess 1106 of the filter assembly. The screen layer1110 can provide support, such as to aid the filter assembly in keepinga desired configuration.

FIG. 11J shows a flow chart depicting a method of making a filterassembly. A filter material can comprise an electrostatic layer and asupport layer. The filter material can be sandwiched between a horn anda nest. The horn can be lowered or otherwise moved into a recess in thenest, thereby configuring the filter material to a shape thatsubstantially resembles the shape of the outer surface of the horn andthe shape of the recess in the nest. The horn can be removed from therecess. The filter material can be configured to substantially retainits shape once the horn is removed from the recess. A screen layer canbe place on top of the filter material. The screen layer can cover aportion of the open side of the filter material. The layers can bebonded, such as by welding, together. The filter assembly can be removedfrom the nest. Excess material can be removed from the filter assembly.

A method for making a filter assembly as described herein is shownschematically in FIGS. 12A to 12G. In this method a sheet of filtermaterial 1202 is provided (FIG. 12A). The sheet of filter material 1202can comprise an electrostatic layer 1220 and one or more support layer1222 (such as a scrim layer). The sheet of filter material 1202 can bewelded in one or more locations, such as along weld line 1214 (FIG.12B). The distance between two weld lines 1214 can differ from a firstsheet of filter material 1202 to a second sheet of filter material 1202.

The method can also include the use of a nest 1204. The nest 1204 cancomprise a recess 1206 (FIG. 12C). The recess 1206 can be shapedsimilarly to the desired final shape of the filter assembly. A firstsheet of filter material 1202 can be placed on the nest 1202. The weldlines 1214 can be perpendicular to the nest 1204. The first sheet offilter material 1202 can be placed on the nest 1204, such that a portionof the recess 1206 is still exposed. In an embodiment an edge of thefirst filter sheet (such as a welded line 1214) is aligned with an edgeof the nest 1204.

The method can comprise the use of a horn 1208 (FIG. 12D). The horn 1208can have a similar shape as desired final shape of the filter assembly.The sheet of filter material 1202 can be positioned between the horn1208 and a nest 1204. The horn 1208 can be pressed into the recess 1206,such as to configure the filter material 1202 into a shape that closelyresembles the recess 1206 and the horn 1208 (FIG. 12E).

A second sheet of filter material 1202 can be placed on top of the firstsheet of filter material 1202, such as to sandwich the horn 1208 inbetween (FIG. 12F). The first sheet of filter material 1202 can bebonded to the second sheet of filter material 1202, such as by weldingalong lines 1214. The horn 1208 can be removed from the recess 1206,such as through the open end of the filter assembly. Removing the horn1208 can define the recess in the filter assembly. Excess material 1216can be removed from the filter assembly, such as by trimming it,resulting in a filter assembly 1200 (FIG. 12G).

FIG. 12H shows a flow chart depicting a method of making a filterassembly. A filter material can comprise a layer of electrostaticsandwiched between two support layers (such as two scrim layers). Afilter material can include two weld lines, such as one at the frontportion of the filter assembly and one at the back portion of the filterassembly. The two weld lines can be parallel. A first sheet of filtermaterial can be disposed on a nest. The nest can comprise a recess. Thetwo weld lines can be positioned perpendicular to the recess. A horn canbe inserted into the recess, such as to form the first sheet filtermaterial to closely match the shape of the horn and the recess.

A second sheet of filter material can be disposed on top of the horn andon a portion of the first sheet of filter material. The second sheet offilter material can comprise two weld lines. The weld lines on thesecond sheet of filter material can be aligned with the weld lines onthe first sheet of filter material. The first sheet of filter materialcan be bonded to the second sheet of filter material, such as bywelding.

The horn can be removed from the recess, such as to define a recess inthe filter assembly. The filter assembly can be removed from the nest.Excess material can be removed from filter assembly, such as bytrimming.

Experiments

In order to evaluate the performance of filters made in accordance withthe present invention, comparisons were made between two comparativerecirculation filter elements, and two filter elements made inaccordance with the present disclosure.

In the first comparative example, the filter element was a substantiallyplanar recirculation filter with a polypropylene scrim overlying anelectrostatic media. The polypropylene scrim had a permeability ofapproximately 300 feet per minute at 0.5 inches of water. Theelectrostatic media had a permeability of approximately 400 feet perminute at 0.5 inches of water. The filter element did not contain anadsorbent material.

In the second comparative example, the filter element also was asubstantially planar recirculation filter with a polypropylene scrimoverlying an electrostatic media. The polypropylene scrim had apermeability of approximately 500 feet per minute at 0.5 inches ofwater. The electrostatic media had a permeability of approximately 400feet per minute at 0.5 inches of water. The filter element did notcontain an adsorbent material.

In the single recess filter, a filter element made in accordance withthe present disclosure was produced, the filter element having asubstantially conical shape. The filter element included anelectrostatic media overlying a polypropylene scrim on the interior ofthe filter element. The electrostatic media had a permeability ofapproximately 400 feet per minute at 0.5 inches of water. Thepolypropylene scrim had a permeability of approximately 500 feet perminute at 0.5 inches of water. The filter element did not contain anadsorbent material.

In the multiple recess filter, a filter element made in accordance withthe present disclosure was produced, the filter element had multipleelongate recesses that were substantially parallel to one another. Thefilter element included an electrostatic media overlying a polypropylenescrim on the interior of the filter element. The electrostatic media hada permeability of approximately 400 feet per minute at 0.5 inches ofwater. The polypropylene scrim had a permeability of approximately 500feet per minute at 0.5 inches of water. The filter element did notcontain an adsorbent material.

TABLE 1 Ratio of Percent of Percent of Percent of Trapped to ParticlesParticles Particles that Reflected Reflected Trapped Fall Out ViewParticles Comparative 38.0 29.0 33.0 .76 Example 1 Comparative 35.0 16.049.0 .46 Example 2 Single Recess 34.2 26.7 39.2 .78 Filter MultipleRecess 20.0 48.3 31.7 2.42 Filter

As indicated in Table 1, the filter constructions with recesses andexposed electrostatic had lower particle reflection rates, and also hadhigher ratios of trapped to reflected particles. Table 1 shows that thatthe percent of particles reflected from the filter elements was lowerfor the two elements made in accordance with the present disclosure thanthe two comparative examples: 20.0 and 34.2 compared to 35.0 and 38.0.In addition, both filter elements made in accordance with the presentdisclosure showed a higher ratio of trapped to reflected particles: 2.42and 0.78 compared to 0.76 and 0.46. Thus, the two example elements madein accordance with present disclosure demonstrated improved removal ofparticulate contaminants compared to the two comparative examples.

The above specification provides a complete description of themanufacture and use of the invention. Since many embodiments of theinvention can be made without departing from the spirit and scope of theinvention the invention resides in the claims hereinafter appended.

1. A filter assembly for use in an electronic enclosure, the filterassembly comprising: a first sheet of filter material defining includingan open front face, a closed rear face, and an internal recess, whereinthe first sheet of filter media comprises a scrim material and anelectrostatic material at least partially covering the scrim material;and a second sheet of filter material disposed over the open front faceand bonded to the first sheet of filter material.
 2. The filter assemblyof claim 1, wherein the scrim material comprises a woven material. 3.(canceled)
 4. The filter assembly claim 1, wherein the scrim materialcomprises polypropylene fibers.
 5. The filter assembly of claim 1,wherein the scrim material has a permeability of between about 100ft./min. at 0.5 inches of water and about 800 ft./min. at 0.5 inches ofwater. 6-7. (canceled)
 8. The filter assembly of claim 1, wherein theelectrostatic material comprises a mixed fiber medium comprisingpolypropylene and acrylic.
 9. The filter assembly of claim 1, whereinthe electrostatic material has a permeability of between about 250ft./min. at 0.5 inches of water and about 750 ft./min. at 0.5 inches ofwater.
 10. The filter assembly of claim 1, wherein the electrostaticmaterial has a filtering efficiency of about 20% to about 99.99% for 20to 30 micron particulate contaminants.
 11. The filter assembly of claim1, wherein the internal recess has a ratio of maximum length to maximumdiameter of the open front face of at least 1.0. 12-13. (canceled) 14.The filter assembly of claim 1, wherein the internal recess of thefilter assembly has an internal surface area that is at least 2 timesthe area at the open front face. 15-21. (canceled)
 22. The filterassembly of claim 1, wherein the filter assembly comprises arecirculation filter disposed within a housing of a disk drive, and thefilter assembly is oriented to filter airflow induced by the rotation ofone or more disks within the disk drive housing. 23-56. (canceled) 57.The filter assembly of claim 1, wherein the second sheet of filtermaterial comprises a scrim material and an electrostatic material atleast partially covering the scrim material.
 58. The filter assembly ofclaim 1, wherein the second sheet of filter material comprises a screenlayer.
 59. A method of making a filter assembly comprising: forming afirst sheet of filter material to substantially retain the shape of aninternal recess, wherein the first sheet of filter material comprises ascrim material and an electrostatic material at least partially coveringthe scrim material; positioning a second sheet of filter material overthe internal recess; and welding the first sheet of filter material tothe second sheet of filter material around the internal recess.
 60. Themethod of claim 59, wherein forming the first sheet of filter materialcomprises positioning the first sheet of filter material between a hornand a nest and applying force such that the first sheet of filtermaterial substantially conforms to the shape of the nest.
 61. The methodof claim 59, further comprising forming a border around the internalrecess of the first sheet of filter material.
 62. The method of claim61, wherein forming a border comprises applying sonic energy to thefirst sheet of filter material.
 63. The method of claim 59, furthercomprising trimming the first filter material and the second filtermaterial extending beyond the welding of the first filter material tothe second filter material.
 64. The method of claim 59, wherein thesecond sheet of filter material comprises an electrostatic layer and ascrim layer.
 65. The method of claim 59, wherein the first sheet offilter material comprises an electrostatic layer positioned between twoscrim layers.
 66. The method of claim 59, wherein the electrostaticmaterial is positioned within the internal recess of the first sheet offilter material.